The proposed investigations involve social factors and genetics influencing puberty in mammals. The investigations have potential significance and application in three areas of behavioral biology and development. (1) Generation time is a critical parameter in population biology. Aspects of two distinct models of population regulation via changes in generation time will be tested by several experiments. (2) Knowledge that chemical stimuli affect social behavior in mammals, including man makes it very necesseary to conduct experiments on pheromone production and effects on behavior and physiology. (3) Menarche in human females occurs earlier than 150 years ago. Studies of factors affecting puberty culd provide information that is helpful in explaining this shift. Proposed experiments will utilize house mice as subjects and first vaginal estrus as a dependent variable for puberty. The two major goals are to obtain an understanding of ways in which social and genetic factors affect puberty and to test several aspects of two possible models for population regulation. Four major lines of experimentation are planned; (1) experiments on social factors affecting flexibility of puberty in two stocks of mice previously selected for early and late sexual maturation, (2) studies of various aspects of acceleration and delay of puberty as they pertain to population regulation, (3) investigations of mechanisms of male acceleration and female delay of puberty in laboratory mice, and (4) an artificial selection experiment to assess genetic inheritance affecting puberty in wild house mice.